SHANGHAI — Within its digital borders, China has long censored what its people read and say online. Now, it is increasingly going beyond its own online realms to police what people and companies are saying about it all over the world.

For years, China has exerted digital control with a system of internet filters known as the Great Firewall, which allows authorities to limit what people see online. To broaden its censorship efforts, Beijing is venturing outside the Great Firewall and paying more attention to what its citizens are saying on non-Chinese apps and services.

As part of that shift, Beijing has at times pressured foreign companies like Google and Facebook, which are both blocked in China, to take down certain content. At other times, it has bypassed foreign companies entirely and instead directly pushed users of global social media to encourage self-censorship.

This effort is accelerating as President Xi Jinping consolidates his power. The Chinese leadership is expected to officially abolish term limits at a meeting that begins next week, giving Mr. Xi outsize authority over the country’s direction.

Zhang Guanghong recently discovered the changing landscape for technology firsthand. Mr. Zhang, a Chinese human rights activist, decided last fall to share an article with a group of friends side and outside China that criticized China’s president. To do so, he used WhatsApp, an American app owned by Facebook that almost nobody uses in China.

In September, Mr. Zhang was detained in China; he is expected to soon be charged with insulting China’s government and the Communist Party. The evidence, according to his lawyer, included printouts of what Mr. Zhang shared and said in the WhatsApp group.

That information was likely obtained by hacking his phone or through a spy in his group chat, said China tech experts, without involving WhatsApp. Mr. Zhang’s case is one of the first-known examples of Chinese authorities using conversations from a non-Chinese chat app as evidence — and it sends a warning to those on the American platform, which is encrypted, that they could also be held accountable for what’s said there.

“China is increasingly throwing its weight around,” said Joshua Rosenzweig, an analyst at Amnesty International.

As Mr. Xi asserts himself and the primacy of Chinese geopolitical power, China has also become more comfortable projecting Mr. Xi’s vision of a tightly controlled internet. Beijing had long been content to block foreign internet companies and police the homegrown alternatives that sprouted up to take their place, but it is now directly pressuring individuals or requesting that companies cooperate with its online censorship efforts.

That puts many American tech giants in a tricky position, especially those that want access to China’s vast internet market of more than 700 million strong. In the past, these companies have typically gone to great lengths to gain a toehold in China. Facebook created a censorship tool it did not use and released an app in the country without putting its name to it. Apple is moving data storage for its Chinese customers into China and last year took down software that skirts China’s internet blocks from its China App Store. Google recently said it would open a new artificial intelligence lab in the country.

Often, these companies have little recourse when pressured for help by Beijing. Going to the American government could set off retaliation from China, so many have sought to navigate the situation on their own.

“I personally am not sure what the solution is for these companies,” said Mr. Rosenzweig. “I don’t see a good answer because the Chinese government is really putting them between a rock and a hard place.”

China leaned heavily on major internet companies when Guo Wengui, a Chinese tycoon in self-imposed exile, went on Facebook and YouTube to accuse a number of Chinese officials of corruption. Chinese officials last year complained to Google, which owns YouTube, and Facebook, according to people familiar with the events who requested anonymity because they were not authorized to discuss the issue publicly.

Facebook suspended Mr. Guo’s account. In a statement, the company said the account published the personal information of others without their consent, which violated the platform’s policies. A spokeswoman declined to comment on whether Beijing’s complaints played a role.

Chinese authorities have also successfully persuaded Google to pull down content that had been available around the globe.

The Chinese government asked Google’s services to take down 2,290 items in the first half of last year, according to the company’s statistics. That was more than triple the number it requested in the second half of 2016, which itself had set a record.

Content related to terrorism made up a substantial portion of the material China asked Google to take down, according to its data. The majority of China’s recent takedown requests focused on videos on YouTube, the data showed. A Google spokesman said the company would not comment further on specific takedown requests.

Chinese officials may have even bigger censorship ambitions.

At a major Chinese internet conference last year, Mei Jianming, a Chinese antiterrorism expert, said Beijing should put more pressure on companies like Twitter. The goal would be to get them to change their terms of service so they could restrict posts by groups that Beijing considers subversive, like the World Uyghur Congress, which seeks self-determination for the people of the western Chinese region of Xinjiang.

Mr. Mei called for a crackdown on tweets that “defame the party, Chinese leaders, and related national strategies.”

Sometimes, Chinese people also push foreign companies to censor themselves in the country, nurtured by sentiments on China’s propaganda channels.

Daimler, the German carmaker, apologized in February after its Mercedes-Benz brand posted an inspirational quote on Facebook’s Instagram that it attributed to the Dalai Lama. China’s government views the Tibetan Buddhist leader as a champion of independence for Tibet, and Mercedes-Benz faced withering criticism from Chinese online users who shared those views.

Mercedes-Benz erased the post — even though few people in China could see it because Chinese authorities block Instagram. Still, criticism continued. The People’s Daily, the official newspaper of the Communist Party, branded Mercedes-Benz an “enemy of the people.”

China is Mercedes-Benz’s biggest single car market, accounting for about one-quarter of sales.

“China is getting stronger,” said Lokman Tsui, a professor at the School of Journalism and Communication at the Chinese University of Hong Kong, and a former Google employee. “They’re getting more confident in putting pressure on these platforms.”

China is also requiring individuals to the police what they say on global social media. In a prominent conviction last year of a human-rights activist, Lee Ming-che, the Chinese police used writing that he had posted on Facebook from Taiwan as evidence against him.

“The fact that China is punishing people for critical content published outside China to audiences not based in China is of course a concern,” said Mr. Rosenzweig.

The case of Mr. Zhang, the Chinese individual under scrutiny for what he posted on WhatsApp, could indicate a further extension of China’s reach.

The Chinese police have previously focused on activists for what they say on foreign social media, but Mr. Zhang’s case seems to be one of the first in which someone has been charged for spreading articles on WhatsApp. Because WhatsApp is encrypted and run by a foreign company, it is generally considered a safer platform than local messaging app WeChat, which has for years been closely monitored by Chinese authorities.

Mr. Zhang’s lawyer, Sui Muqing, said he was surprised when the police presented him with printouts of articles and comments from Mr. Zhang.

“They didn’t get the information from him, but they have it,” Mr. Sui said. “That was what we found so weird. None of us knew how they were capable of getting that data and whether WhatsApp has become unsafe.”

Experts said the information was likely gleaned from somebody within Mr. Zhang’s WhatsApp group or by accessing Mr. Zhang’s phone directly, not by hacking WhatsApp. Chinese officials formally blocked WhatsApp in China about the time of Mr. Zhang’s detention.

A spokeswoman for WhatsApp said Chinese authorities did not have backdoor access to its encrypted messages. China’s Ministry of Public Security did not respond to requests for comment.

“When I talk about technology and the internet, people normally pine for them and look forward to a future that will promote liberalization,” Mr. Sui said. “But people neglect the fact that modern authoritarianism also rises with the development of technology, which makes wider and deeper control possible.”